SBAS940 December 2018 DAC8742H
The primary supply for the transmitter is the TPS7A4101 device, which is a 50-V input, 50-mA Single output low-dropout linear regulator with very low quiescent current, 25 µA. The device supplies a well-regulated voltage rail (1% accuracy), operating within an extended temperature range of –40°C to 125°C, and also withstands and maintains regulation during very high and fast voltage transients. In this design the LDO converts the external supply to a 5-V rail that is used by the DAC8830, LM4132 and OPA333/OPA335. The 200-Ω resistor that separates the loop supply from the LDO acts as a current limiting resistor at startup and additionally improves the overall receiver impedance of the design.
Generally, series references are preferred over shunt references because of their lower power consumption; in this case the LM4132 exhibits a maximum of 60-µA quiescent current. Moreover, the device has an initial accuracy of 0.05% with a specified temperature coefficient of 10 ppm/°C or less, and is capable of operating with these metrics at an extended temperature range of –40°C to 125°C.
In order to generate a 3.3-V supply for the DAC8742H, the TPS7B6933-Q1, a low-dropout linear regulator with low quiescent current, is incorporated into the design. This LDO is capable of operating over a wide temperature range of –40°C to 125°C, while exhibiting a maximum quiescent value of 25 µA over this temperature range.